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VALVE AMP BIASING
IN THE LAST DECADE WE HAVEseen huge advances intechnology which
haveprofoundly changed the way wework. Despite the rise in
solid-state and digital modellingtechnology, virtually every
high-profile guitarist and even recordingstudios still rely on good
olfashioned valves.
What is a valve?Hopefully, a brief explanation willgive you a
full understanding ofwhat is happening inside your ampand the
enigma that engulfs theterm known as biasing. A valve ismade up of
a minimum of fourcomponent parts: the heater,cathode, grid and
plate. They areall housed in a sealed, airlessvacuum and this is
why theAmericans call them vacuum tubes.
The heater warms the cathode,which when heated allows
theelectrons to flow from the cathode(negatively charged) to the
plate(which is positively charged). Thegrid is situated between
thecathode and the plate.By applying
a signal to the grid it causes acurrent to flow from the cathode
tothe plate. The grid is also known asthe control grid, as by
varying thevoltage on the grid you can controlhow much current is
passed fromthe cathode to the plate. This isknown as the grid bias
of your amp the correct bias level is vital to theoperation and
tone of the amplifier.
By varying the negative grid bias the technician can correctly
set up your amp for maximumperformance, thus ensuring thatthe valve
is operating correctly. Thevalve therefore operates literally asa
valve regulating the current flowfrom the cathode to the plate
thats why in England we call it a valve.
What is bias? The amplifier bias, and theproblems associated
with it,confuses many musicians If youthink of a kitchen tap as
avalve and the
water as an electrical current, youwill never be confused again.
Whenyour tap is turned off you get nowater flowing through. With
youramp if you have too much negativevoltage on the grid you will
stopthe electrical current from flowing.This is known asover-biased
and the amp will produce an unbearabledistortion at allvolume
levels.
If you turn your tap full onyou get a huge rushof water. If
youramplifier does not haveenough negative voltage atthe grid then
you will find youhave an under-biased amplifier.This allows too
much current topass through the valve and willcause it to burn out
quickly andyou will lose punch and clarity in
your sound.
Types of biasYou can now see that
the bias of theamplifier affectsits tone. More
interestingly, the type of bias
arrangement that the amplifier
manufacturer choosesalso affects the sound.
Generally there are twotypes of bias arrangement
used in guitar amplifiers. Acathode bias amplifier has a
resistor going from the cathodeto ground. This resistor is set
to
provide the correct current draw ofthe valve by setting the
negativevoltage. This enables the tech to
alter the negative grid voltage byreplacing the resistor to gain
the current draw required.Cathode bias amplifiers havebecome very
sought after. Theyhave a sweet organic sound thathas a rich
harmonic sustain andthey produce a powerfulsoundstage. Examples of
these are most of the original 1950s
Fender tweed amps such as theDeluxe and, of course, the
legendary Vox AC30.In a fixed bias amplifierthe cathode is
grounded and aseparate negative
voltage isapplied to the grid of
the outputvalve. Some
amplifiermanufactures, such
as Marshall, fit a little trim-pot on the negativepower supply.
This allows for easyresetting of bias when the outputvalves are
changed.
In Mesa/Boogie amps no suchtrim-pots are fitted but, contrary
topopular belief, by changing a fewresistors, bias on these amps
can beadjusted. I would always fit a trimpot where possible on
theseamplifiers as it will give you morevalve choice in the longer
term andalso make it easier for a tech to setthe bias. These amps
generally havehigh outputs and more headroomthan cathode bias
amplifiers;examples being Marshall and Boogie.
Matching anddual matchingNow we need to understand theterms
matched and dual
How have valve amps survived over 30 years of change? Derek
Rocco explains why they are still a vital ingredient in music
making, and talks you through the mysteries of biasing
Biasedinformation
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VALVE AMP BIASING
GUITARIST FEBRUARY 2001 139
matched (which are significantlydifferent) when replacing
outputvalves. Output valves will normallylast around two years, but
higherquality British and American valvescan last a least twice as
long, due to better components and build quality.
We are often bombarded withscience and weird and
wonderfulmethods of how to match valves.Simply, the term matched
meansthat when a fixed amount ofnegative voltage is applied to
thegrid, the valve will allow a certainamount of current to flow
throughit. The amount of current allowedby each individual valve
can varysignificantly, and therefore bymatching, or grouping those
withthe same current draw readings wecan ensure that the amplifier
isdrawing evenly with a similarcurrent draw from each valve.
So, having the valves matched (alldrawing the same current),
givesthe amp technician the opportunityto correctly set the
negative gridvoltage so the amplifier functionscorrectly. If the
valves were notmatched, as the technician sets thenegative grid
voltage, they wouldall draw different amounts ofcurrent therefore
making itimpossible for the amplifier to beset-up correctly.
It is very important tounderstand, however, that thismethod of
matching, based on thecurrent draw, is only half the task.Because
valves also have differentoutput levels, when you fire upyour
guitar through the amplifier,valves with different outputs willlead
to the amplifier soundingunbalanced with uneven distortion.
This is why at Watford Valves, forexample, we drive the output
valves
under working conditions and loadto measure the output of the
valve.This is measured in milliamps pervolt and ensures that the
valves alsohave the same output. Thisprocedure enables us to
identifyand supply valves with verydifferent characteristics.
Forexample, valves with a higheroutput will generally distort
sooner,and valves with a lower output willtake longer to distort.
Valvesmatched on current draw andoutput levels are termed as
dualmatched. They will give you a richerharmonic sound, as they
allworking evenly, and theyll preventpremature component wear.
When do I need tore-bias?Having the bias checked shouldalways
happen when you changeyour output valves. Valves that aremade today
are not as consistent asthose produced in the early days ofvalve
production. We quitecommonly see great variancebetween valves from
the samebatch. So to simply buy a matchedpair of EL34s, for
example, even bythe same maker, is no guaranteethat they will work
correctly as theymay draw more or less current anddiffer from the
way in which theamp has been set-up.
The cost of using an amptechnician varies; some offer a
full-service, others will just check thebias setting. The thing to
rememberis that these guys see amps day-inand day-out and they can
preventtrouble happening vital for allgigging musicians.
Valve choiceAnother often used term in relationto valves is New
Old Stock (NOS).
This simply means that the stock isnew but is not of
currentproduction. These valves aregenerally made by British,
Germanand American factories such asMullard, Philips, GE and RCA.
These factories, sadly, no longerproduce valves. But these valves
are the highest quality available asthey were made with very
strictproduction control and high quality components. They are well
worth seeking out. They havea longer life, better tone andsuperb
reliability.
In recent years weve seen theAmericans take over the controland
distribution of a number ofRussian factories, giving rise to
thenames Svetlana and Sovtek. TheTesla factory has also reformed
asJJ. Their valves are very good. TheChinese-made ones, which
plaguedmusicians for many years, nowseem in decline.
Why are valve ampsso popular?A valve amps sound istremendously
flexible and can betailored to the individuals taste.Many valves
like the EL34, 6L6GC,5881, KT66, KT77, KT88 and6550A all share the
same baseconfiguration, yet they all havedifferent sounds and can
be used in
the same amplifiers with only slightmodifications or simple
biasalterations. The classic Marshall JTM 45 with KT66s, and
Malcolm Youngs Marshalls fitted with 6550A are just a couple of
examples.
I believe the main reason somany players still chose
valve-driven product is down to tone. A valve has a clipping point
thatprovides that rich distortion andsound which cant be replicated
by a transistor. Undoubtedly somemanufacturers are now very closeto
replicating the tone of a valveamp with alternate technology but
with minimum impact on thevalve market.
The great manufactures ofyesteryear, like Mullard, Philips, GE
and RCA all used different materials and techniques toproduce
valves. In the same way that a great guitar shapes the tone and
characteristics of your amplifier, so does a valve, so a lot of
thought must be putinto buying valves and thecharacteristics
desired.Musicians have kept valves alive
over the last 30 years and with thecurrent Russian and Eastern
Blockvalves continuing to improve, thefuture looks good. Maybe in
thesedays of samples and MP3 files we
Here are some useful numbers for technicians who
undertakeamplifier biasing
BristolSoundburn AudioJessey James, 0117 955 5766
Beds Bucks & HertsS D ElectronicsSteve Dove, 01442
257269
EireP Keenaham amp repairsPeter Keenahan, 00353 1 671 8886
LondonT A ServicesTheo, 0208 881 1623
ManchesterThe Amp ClinicRoland Lumby, 0161 787 8082
Useful numbers
Preamp valves(front) power outputvalves (rear) next to a
rectifier valve
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GUITARIST FEBRUARY 2001 141
W HEN YOU BUY Amatched set of outputvalves for your amp
younaturally expect them to be tested.In most cases output valves
aresubjected to tests to ascertain thecurrent draw and heater
continuity.These tests give a quick idea ofwhether a valve will
work in aguitar amp or not, but they are along way from ideal.
The kind of punishment a valvegets put through in a real
guitaramp being played loudly is a lot likethe gruelling training
undergone bythe worlds toughest troops. Usingthis analogy, the
majority of valvetesters put their output valvesthrough a days
gentle march in the
army cadets. Watford Valves,however, with the aid of
itscustom-built test rigs, puts thevalves under real
workingconditions which is the equivalent of a hellish week with
the US Navy Seals.
Custom-built rigsThese custom-built test rigs setWatford Valves
apart from otherdealers, says Rocco. They allowcustom selection to
guarantee thatthe valves are less likely to failwhen the going gets
tough. Twoof the most common machines thatare used for testing
valves weremade by AVO (which stands foramps, volts and ohms). The
most
common tester, which was used bymost valve suppliers in the
sixties,was the AVO Mark IV. This machinecan perform many functions
on asingle valve. It was designed for
service stations to check whether avalve had the correct
conformity tothe manufacturers specification.This enabled valve
distributors tomatch valves on the current that it
InsideWatford Valves
Derek Rocco runs Watford Valves in the UK. Ben Bartlett pays him
a visit...
INSIDE WATFORD VALVES
Valves at ease after Roccos rigorous testing
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INSIDE WATFORD VALVES
GUITARIST FEBRUARY 2001 143
was drawing on the tester and sowas born the phrase matching.
Inthe seventies, AVO launched theVCM-163 which was the firstmachine
to allow the output of avalve to be measured accurately,along with
the current draw.
Its clear that although these testers can prepare our troupes
forbattle, they will not prepare themfor the conditions that the
roadwill throw at them: SAS style-training will be needed.
WatfordValves identified this problem atthe beginning of the
nineties.
The company was originally set-up to provide local groups with
areliable source of valves, but itbecame clear that
specialistequipment was needed which wasnot available commercially.
WatfordValves then embarked, withmilitary precision, on a
researchand development programmewhich, by listening to some of
themost-respected technicians in theindustry, has resulted in what
theybelieve is the most advanced test-centre for valve
evaluation.
On with the tests...The first rig Rocco shows to me isthe high
plate volt rig which wasdesigned around Marshall andFender
amplifiers. This rig is aworking amplifier which resemblesa serious
assault course and onewhich all Harma valves, Watfordsown brand,
have to pass. This unittests all output valves from 6V6GTto KT88
and applies to an EL34, forexample, 500V plate and screen.
This procedure sorts the chaff fromthe wheat any weakness or
shortcircuits will cause the valve to fail.
The valves are also tested herefor cathode heater insulation.
Theheater inside is a bit like aminiature electric-bar fire
whichgets the cathode or negative plateup to operating
temperatures. Ifthe insulation of this component ispoor the valve
will hum unfortunately, itll be humming adifferent tune from the
one youwant to play! This tester also has amicrophonic test for
output valveswhich was designed around a
Fender Twin, as this is one of themany tests that the AVO
simplycannot do.
Although our American chumscall valves vacuum tubes, thevacuum
isnt always as perfect as it could be. If the valve isgassy it has
too much air inside the life and the gain of the valve are
significantly reduced,thus resulting in poor sound.Watford Valves
prefers not to useChinese-made valves, believingthat a lot of them
suffer from agas problem and that they have ahigh failure-rate.
Regular supplyThe second test-rig takes the rangeof the first
rig a stage further withthe inclusion of digital meters anda signal
generator. Here I see whyit is so important to regulate themains
supply these digital metersare so accurate that a change inthe
supply can change a valvesreading drastically. The principlehere is
simple: there is no pointlearning to fire a pistol and thenbeing
expected to use a semi-automatic. So, each valve has to be tested
under real workingconditions to measure not only the current drawn
but also theoutput of the valves.
This is vital, explains Rocco.Valves with the same currentdraw
will have different outputs; if the valves have different outputs
then they can sound oddand dramatically affect the soundand balance
of the amp, therefore all output valves arematched on current draw
andoutput/gain. These rigs have biassetting which are the same
asBoogie, Fender and Marshall,
thus insuring more meaningfulreadings, unlike the AVO
testers.
Brian MayRocco now informs us that theprototype rigs have
beendeveloped into two modular blocks which handle 30
valves-per-block, each valve individuallytested for all the above
parameters.In any army, some troops need tobe sent for special
applicationtraining and in this case it does not get any tougher
than the wayin which Brian May, for example,drives his valves in
his AC-30. So
I couldve sworn that thatone just moved. TirelessRocco keeps
watch
Solitary scrutiny on thistest rig equals top qualitytone and
performance
Watford Valves was set up to help local groups. It soonfound
there was a high demand for its specialist equipment
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INSIDE WATFORD VALVES
what hellish device hasWatford Valves come up withto drag those
screaming EL84sand make them come of age?
Conventual testing wassimply not enough, we had toreplicate what
was actuallyhappening in Briansampexplains Rocco. Hesimply runs his
valves so hardthat they are at the point ofdestruction this
contributesto his famous trademarksound. The test rig had to
bedesigned to replicate sustainednotes, single runs and
powerchords. This was a mammothtask and we needed the best,so in
came Dave Petersen thecountrys leading Vox expert.
Enter the full drive bursttester, the Hammer house ofhorror to
all little EL84s. Thetester is a 10 valve AC 30 witha signal
generator providingthe most destructive May-typesignal. A timer is
includedwhich alters the signal fromshorts bursts to long
sustainingnotes. This is the only tester ofits type in the world
and wasdesigned and built in good oldBlighty. Only the
strongestsurvive and while WatfordValves goal of supplying themost
reliable valves for Voxamps has been achieved, thefailure rate is
high as the EL84 graveyard proves.
Mission timeFinally, we come to a totallyunique tester. This
drive testingrig puts the small ECC83/12AX7 through a
real-lifemission. The ECC83/12AX7 isthe most commonly usedpreamp
valve andunfortunately is the mostvariable. The tester runs
thevalves under the sameconditions they would meet inyour amp. The
valves are firstly tested for hum and
electrode noise any faultshere and the valve is given
itsmarching orders.
They are then tested formicrophony. Now, microphonyis not just
reserved for guitarpickups, your valves can starthowling too so the
valves are
linked to an amplifier andspeaker and are checked tosee whether
they would begood in a guitar amp. Thevalves are then tested for
thebalance between the triodes.Most preamp valves are madeup of two
separate halveswhich function best when theyhave the same value in
termsof gain and output.
Once the chosen few havecome this far then the finaltest comes
into play, the drivetest. This test measures theactual
amplification of thevalve with the guitar signaldriven into it.
Each half of thevalve is given a three digit
code. The valves at the higherend of the scale will break
intodistortion a lot faster andprovide you with more gain;lower
values mean that thevalves will stay cleaner as theyare harder to
distort.
Next time you need to re-valve your amp, think on. Arethose new
shiny bottles up toyour demands?
(Left) A Variac regulates the mains supply; (right)quality
valves of yesteryear
The unique drive testing rig putsthe kit through a real-life
mission
Well done my pretties, youve passed the test
G
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A M P T E C H
VALVESU-Like
THE HUMBLE VALVE IS WIDELY ACCEPTED as the mostinfluential
single component of a good guitar amp, but how dothese little glass
bottles work and why are they so important. DaveHunter visits ace
British distributor Watford Valves for a look at allthings tubular,
including the Brian May testing rig...
B DISTORTION
VALVES?
ack in the mid-60s whentransistors appeared to be
theamplification technology of thefuture, the guitar amp
industrystarted trying to sell the publicon lines like
.durability-low
maintenance-no tubes to burn out andreplace. Devoted music
engineers andinsiders knew, of course, that much of it wasjust
marketing speak: wrapping up acheaper-to-produce product as
progressand technological advancement (90scomputer boom and planned
obsolescence,anyone). Long-time Leo Fender cohort andlegendary
engineer Forrest White resignedfrom Fender in December 1966 when
CBSexecs tried to force his hand on solid stateproduction. Fender
went ahead without him,and guitarists - in an era when
Hendrix,Townshend, Clapton, Beck and others werereaching new
heights of lusciously distortedvalve amp tone - fled from tranny
amps intheir droves. These new amps were differentin a lot of ways,
but the single mostsignificant omission? .
In order to lift the lid on these mysteriousglass bottles, TGM
visited Derek Rocco ofWatford Valves in St. Albans. As one of
theUKs premier valve retailers and the mostthorough valve tester in
Europe, he waskeen to help us discover whats behindWatfords raison
detre, and to unveil thecomplexity and variety of the valve
market
as we approach the Millennium.
I think in a nutshell whats important is howthe valve distorts,
says Rocco. When youpush a transistor into distortion, when
itclips, it just shuts down - it doesnt seeanything at the peaks
and troughs of thesine wave (figure 1). With a valve you getthat
harmonic distortion happening as thevalve slowly goes into
distortion. The more itdistorts the more it clips, giving
thatcompression and distortion that everybodyloves.
Even with valve amp settings wedconsider clean, a certain amount
of smooth,rounded distortion adds texture andharmonic richness to
the sound, along withsome valve-induced compression whichmakes the
tone feel more tactile andplayable, and warmer to the ear. Thats
whyvalves have survived, adds Derek, and, Ithink, solely because of
the guitar world.Weve got a huge valve hi-fi market now, butit was
guitarists who recognised how greatvalves could sound when
everything elsehad gone over to solid state.
Inside your amp the guitar signal is handledas a flow of
electronic current; inside the
Valves
HARMONIC
TUBES?
valves themselves this takes the form ofelectrons flowing from
the cathode to theplate (see figure 2 for the constituent parts)-
all of which means little to us out ofcontext.
Basically, a valve amplifies the signal,explains Rocco. One way
to look at it is toexamine why we call it a -valve-. TheAmericans
call it a -vacuum tube- becausetheres a vacuum in that bottle, but
what itbasically does is - and its probably a morelogical way of
describing it - is its anelectronic valve. Just as your
centralheatings water valve can limit the amount ofwater flowing
through the system, electronicvalves can limit or increase the
currentflowing through them.
As the major handlers of current flowwithin the amplifier, the
valves play a big partin shaping the resultant tone. Valves
withdifferent characteristics shape the sounddifferently; the
ultimate conclusion of thisthinking is the fact that, while you can
putany functioning valve of the right type in youramp and it will
work, in order to get itperforming at its peak and sounding just
theway you want it, it pays to put a little extrathought into your
valve buying.
Even though the best valve manufacturers(mainly European and
American) shut downin the 70s, 80s and early 90s as westernindustry
- and, significantly, the military -turned more and more to solid
statecomponents, a great number of generallyexcellent NOS (New Old
Stock) valves
TESTING, TESTING
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Fig. Inside a Preamp Valve2
remain available from makers like GE, RCA,Mullard, Brimar,
Philips and others. All newlymade valves currently come from
factories inEastern Europe or China. Not only dodifferent makes
have somewhat differentcharacteristics, but wide tolerances
withinthe industry often mean that even valves ofone type from the
same factory can soundand perform very differently. In either
case,as with any product turned out en masse,there are also a
certain number of duffvalves in any batch to come off theassembly
line; sadly, plenty of these seem toslip past the factory and/or
wholesalers(sometimes, admittedly, limited) qualitycontrol and into
the marketplace.
The only way to weed out the clunkers isto test them
individually; and while
undertaking such quality tests, someretailers - Watford Valves
and Groove Tubesamong the very few in the world - also testtheir
valves along further parameters whichhelp to quantify their tonal
characteristics.
Whats driving me is the goal ofproducing the best-tested valves
in theworld, says Rocco. Weve had theopportunity of working with
people like BrianMay, Manic Street Preachers, Kula Shaker,Thunder,
Lighthouse Family and others -touring musicians, who need to rely
on thequality of the valves in their amps.
While tube testers have existed for aslong as tubes have been
manufactured,Roccos drive to further quantify their qualityand
characteristics led him to obtain - and insome cases, to have
custom-built - valve
Fig. Valve vs. Solid State Distortion1
testers that go well beyond good valve/badvalve.
We had our preamp valve testerdesigned and built especially for
us,explains Rocco. The resultant rig holds 50preamp valves of types
such as ECC83(called 12AX7 in the USA), 12BH7, 12DW7and others, and
runs them through morechecks than any other testing facility in
theworld, even that used by famous Californiaretailer Groove Tubes.
This is an actual,working amplifier with the same loadingsyoud find
inside your guitar or bass amp,and we drive an actual signal into
eachvalve. We put them through a range of teststhat are relevant to
musicians. Theseinclude:
drive - the power/gain factordistortion - the point at which
they cross
over into distortionhumbalance - valves like ECC83s are
called
dual triodes because they contain two smallvalves within one
bottle; for optimum
nn
nn
Connections
Derek Rocco mans the 50-valve big
rig in Watford Valves testing room.
PLATE (ANODE)
GRID
CATHODE
=FLOW OF ELECTRONS
CROSS-SECTIONVIEW
12AX7/ECC83 TYPEDUAL TRIODE VALVE
CLIPPING
CLIPPING
SIGNAL PEAK
SIGNAL PEAK
HARSH DISTORTIONOR NO SIGNALSINE WAVE:
SOLID STATE
SINE WAVE:VALVE
MUSICAL DISTORTION
WWW.WATFORDVALVES.COM
Digitally matched and gradedvalves for the music industry
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Amp Helpline: Biasing
performance in the amplifier circuit the twohalves should be
balanced
microphony - susceptibility to vibrationdisturbance and
feedback
noise
The main thing were looking at, beyond thebasic function and
whether the valve is noisyor not, is drive. The drive scale runs
from 0to 300. For good, basic valves were lookingfor 170-180. For
an excellent first drivervalve for a Marshall, say, you might
wanteach half of the triode to be 250 - but youllfind out of a
whole batch of good valves, notmany will read that high. We
selected abatch of preamp valves for Kula Shakerrecently, and they
were all 270 and 280!
Output (power amp) valves of the 6L6type (which includes 6550s,
5881s andothers) are run on another specialised rigwhich tests for
gain, distortion, hum andmicrophony. These are driven at a
whopping500+ volts, close to or above the levelsrunning within
actual amps, to determinecurrent-draw levels for accurate
matching(for the importance of output valve matching,see Biasing
sidebar).
When it comes to pinpointing premiumexamples of the
sweet-sounding, small-bottled EL84 output valves, however,Watford
Valves are driven by a highercalling. We were supplying valves for
BrianMays Vox AC30s, and we found they werefailing at an alarming
rate, says Rocco.Brian runs his AC30s flat-out, with a
treblebooster going into the front end, andanything but the
sturdiest EL84s just canttake it.
To isolate valves that are up to the job,Watford built yet
another custom rig, thistime with the help of TGM contributor
andpremier Vox technician David Petersen.
David is brilliant, enthuses Rocco. Heworked out all the
parameters for this testeraccording to whats actually going on
insideBrian Mays amps. We power up 12 at atime, and while were
burning them in underload a timer puts signal surges through
themevery few seconds for an extended period oftime. Any weak ones
will blow, and wellweed them out.
MAY
n
n
DAY
Batches of EL84s tested in this way havebeen sent to May for
months now, to thegreat satisfaction of the man himself - andthe
even greater relief of his amps.
To capitalise on their valve-testingexperience, Watford have
recently launchedtheir own high-end range, branded asHarma Diamond
Range valves. Our goal,Rocco admits, is to one day be
ratedalongside Groove Tubes, but to still be ableto sell valves
cheaper than they do -although many Harma valves are alreadytested
to more stringent parameters. What
we want to achieve is an affordable way totest all our valves
for quality, then the Harmarange will be a select valve that will
combineconfidence in how its been tested with theknowledge that its
different from anythingelse on the market.
The downside is, the more rigoroustesting we do the more valves
we comeacross that fail our standards; so weveapproached it from
the perspective of -whats the best sounding- rather than just
-whats the cheapest or most readilyavailable wholesale valve-.
What a full range of testing allows us todo, however, is to
offer quality guaranteeson all valves but, for a little more
money,also offer valves that have been tested andgraded more
rigorously - for more headroomor more distortion, use in Fenders
orMarshalls, and so forth. That allows us totailor valves to a
variety of specialistapplications and sounds.
For more information on Watford Valvesand the Harma Diamond
Range, contact:Watford Valves 01923-893270, or visittheir Web
site:
%www.watfordvalves.com
What is this thing called biasingthat were meant to have
donewhenever we change power
valves, and whats it all about?
Think of your amp as the engine on anolder model car, explains
DerekRocco. Changing the valves is like
putting in new spark plugs, points andcondenser, but in order
for things to runsmoothly you still have to set the timing andidle
control. Biasing simply sets theoperational level of your
amplifiers outputvalves. Preamp valves, note, are self-biasing -
and therefore excuse themselvesfrom the discussion from here on
in.
All valves of the same type may be madeto the same general
specs, but they comeoff the assembly line with slight
variationsmeaning that, plugged straight in, they wontnecessarily
draw the same current as thevalves youre replacing. The negative
gridbias setting affects the current flowing fromthe plates of the
power valves: increasingthe negative grid bias means less
currentflows through the valve, while decreasing itmeans more
current will flow. Why is thisimportant?
If you have too much current flowingthrough your valves you will
run them andyour amp hot. This will result in burning thevalves out
prematurely and can even riskamplifier and/or transformer damage,
saysRocco. If your amp is running with notenough current flow then
the valves will not
have enough time to correctly amplify thesignal, resulting in
weak tone and a horribleun-musical distortion which is hard on
theear.
The importance of correctly biasing youramp also brings us to
the subject ofmatched power valves. Most amps providea single
facility for bias adjustment, eventhough they may carry a pair or a
quartet ofpower valves. Because the amp must be seta single
negative grid bias level that bothvalves are happy with, its
important toinstall matched sets with similar currentdraw levels.
Slightly mismatched powervalves may work, but the push-pull
circuitryin the amp will operate inefficiently, possiblyresulting
in impaired tone.
Some amps are built with fixed-biascircuits - notably many by
Vox andMatchless (the classic old and new Class Adesigns), some
older Fenders, and evenearlier Mesa/Boogies - so they cant
beadjusted anyway, though matching outputvalves remains vital to
keep the push-pullcircuit at its peak.
NOTE: Biasing - which involves workingwith potentially lethal
voltages - is aprofessional job only. Dont attempt ityourself
without proper training, the correcttools and equipment, and full
safetyprecautions. An amp tech should chargebetween 10-30 pounds to
correctly biasnew power valves (and may include it aspart of a
general service and re-valving job)
-
Tubes are tubes, right? Sadly, no.Guitar amps may function in
theliteral sense with an appropriatetype from any manufacturer
(thoughnot for long in some cases), but becausepreamp and output
valves really are at thecentre of an amps tone, the soundproduced
can alter beyond recognitionfrom make to make.
In simple terms, valves available to buytoday come from two
distinct camps:current production examples, and NewOld Stock (NOS).
The first aremanufactured in factories that are still upand
running, while the second batchconsists of remaining stocks of
valveswhich are still new in the sense thattheyve never been used,
but weremanufactured long ago sometimes asfar back as the 50s.
Valve production in Western Europeand the USA ceased in the
1980s, bywhich time the technologies that primarilysupported it
mainly military andcommunications uses had changed overfrom vacuum
tube to solid state circuitry.Although valves were and still are
used inbetter instrument amplifiers and somehigh-end audio, these
markets justwerent enough to keep the high-costfactories running.
From that point onward,
new valves were only manufactured inEastern Europe and China.
With Chinarecently having ceased production,current manufacture
comes only from theSovtek and Svetlana factories in Russia,JJ Tesla
in the Slovak Republic, and EI inYugoslavia (though availability
and qualityof EI are being hampered by wartimeembargoes, so we wont
consider themhere).
Not a lot to choose from, youll agree.Fortunately considerable
if ever-dwindling supplies of generally superiorNOS valves do
remain, but if youvestudied your economics youll alreadyhave
guessed that the laws of supply anddemand dictate that these
desirableWestern European and US manufacturedcomponents will
gradually commandhigher and higher prices as they sell outinto
extinction.
Thats the reason you really need toknow what youre paying for
and why. Inthe tests below, well look at the mostcommon and readily
available currentproduction preamp valves and a basket ofstill
relatively easily found NOS examples,along with a couple fetching
astronomicalprices but worth considering asstandards of the type
the legendaryMullard, for example.
TESTING: 12AX7/ECC83In order to test the full range
ofapplications, the amplifiers used were a70s Fender Twin Reverb
fitted withJBLs, a 70s Fender Twin Reverb fittedwith original
Fender blue backspeakers, a Mesa/Boogie Mark IVcombo, a Marshall
100 Super Lead into a4x12" cab, an 80s Fender PrincetonReverb II
and a vintage Vox AC10 withElac speakers. Guitars used included
a1973 Fender Stratocaster, 1980 YamahaSA 2000S semi-acoustic and a
1980Gibson Les Paul Standard. Valves wereselected for low
microphony and lownoise and rated for gain.
All of the valves below are of the12AX7/ECC83 double triode
type(12AX7 being the US designation, ECC83the European). While you
will find othervalve types in some parts of guitarpreamps, these
are the most commonfirst gain stage choice and thereforehave the
most effect on your amps driveand tone. Origin and Current or
NOSmanufacture are indicated; GP stands forGuide Price and gives an
approximaterange of prices commanded by eachvalve type on todays
market. Forspecific prices and availability, checkwith retailers in
our Connections sidebar.Any letters or numbers following
themanufacturer name (such as WA orLPS) indicate sub-codes in the
valvetype ie 12AX7LPS. Mullard ECC83,Mullard M8137 Box anode, RCA
7025and Telefunken ECC83 were used as thereference.
SYLVANIA (USA, NOS. GP: 9 16)Classic American valve which was
fittedby all the great 60s amplifier companiessuch as Ampeg, Fender
& Gibson. Thisvalve produces a rich, warm sound withexcellent
balance; when distorted itproduces a fat sound with plenty of
drivewithout loss in top end clarity. In theFender amps the valve
produces a clean,bright response which is great forfingerpicking.
Single coils sound full withno harshness and plenty of detail.
In the Boogie a sweet, crisp cleansound is easily attained, plus
a classicrock sound with a little mid-forwardness(which we like).
Because of the high-gainnature of the Boogie, however, itsimportant
to select valves for lowmicrophony. Early 1960s production; anideal
choice for all vintage Fenders.
GE-JAN (Joint Army Navy) WA (USA, NOS. GP: 8 25)This rugged
American military spec valveis of immense quality its the samevalve
fitted as standard in 70s Fenders.The GE valve is famous for its
big, crisp
A M P T E C H
78
TUBETastingA Players Guide: Pt1 Preamp ValvesJUST AS DIFFERENT
STRINGS OR PICKUPS WILL DRASTICALLY alterthe sound of your guitar,
different makes of even the same typeof valve can radically change
your amps tone and affect itsreliability. British dealer and
premier tube tester Derek Roccoof Watford Valves shares his taste
tests with us
-
sound stage and bright top endresponse, something which
reallybreathes life into Fenders. This valvesupplies that authentic
Fender twang; itsbrighter than the other American valvesand also
works really well in the Vox bygiving it a clearer top end
response.When the valve distorts it has a richharmonic feel and
chime. Even underheavy Boogie distortion the bass andmidrange
detail are superb. Thoroughlyrecommended.
SOVTEK WA(Russia, current. GP: 3.50 6)Low to medium gain with
the samesound quality and less gain than the WB.When distorted, the
WA doesnt have thedetail or balance of NOS stuff this valveseems to
be pushing everything throughthe mid band. When pushed hard
thesound compresses very early, too. Butits good for general
repairs.
SOVTEK WB(Russia, current. GP: 5 8)Low to medium gain with
lowmicrophonics. Clear, bright sound,
although it lacks the clarity and definitionof NOS valves, and
it and distorts earlierthan the WA. The sound is the same asthe WA,
but far better than the Chinese12AX7 no snap, crackle and pop.
SOVTEK LPS (Russia, current. GP: 8 10)The new Sovtek 12AX7LPS is
now inproduction in Russia. This valve is ofmedium to high gain and
has a specialspiral filament which greatly reduceshum when
operating in amplifiers withAC heaters. This is certainly the
best12AX7 that Sovtek have come up with.
In guitar amps we noticed that thelevel of microphonics are
higher than theWB, but this would also be consistentwith the higher
gain of the tube. It gives abright and clean sound, but not as
sharpas the GE (below). When distorted, itretains its control and
sounds sweet.Overall this is a very good sounding valve a decent
choice for audio or guitar.
PHILIPS-JAN WA(USA, NOS. GP: 7 14)Low-noise American military
valve made
in the famous Sylvania plant inEmporium, Pennsylvania. It
retains theclassic warm, solid sound of the earlySylvania but has
less drive. This provesuseful in the Boogie as the lower gain ofthe
valve gives less microphonics.Midrange is very musical with all
theclarity of the Sylvania.
The bottom end is superb: incomparison to the Sylvania it sounds
alittle tighter and better defined, which iswelcomed in the
Marshall amps. Thebass is not as deep as the Mullard butthe Philips
does have that instant British-style tone. In the Fender amps all
thetone that you would expect is there. Thisis a superb valve and
an instant upgradefor all modern amps.
MULLARD(GB, NOS. GP: 35 60)This legendary British valve is the
mostsought-after ECC83/12AX7 type of alltime. The key is the way
the valvedistorts. The Mullard reproduces exactlywhat is driven
into it with greatmusicality, combining smooth drive withbalanced
low microphonics andreproduces every subtle detail with a rich
79
Sovteks lower-gain WA
The real McCoy: British and US-madeNOS valves by GE, RCA and
Mullardare the stuff of ampaholics dreams
A more desireable Sovtek WB
-
sound stage. When overdriven the valvehas a 3-D effect which
makes it reallysing and it sounds amazing in a Boogie.The noise
level even at full saturation isvery low, while the bass response
hasgreat kick without loss of definition. Wecame to the conclusion
that this wasgoing to be a hard act to follow.
BRIMAR CV4004(GB, NOS. GP: 11 24)British military spec valve
with half-flangeanode giving instant British rock.Exceptional
balance and sound stagingwith great drive. It hasnt got the
richharmonic distortion or the unique 3Deffect of the Mullard and
under fulldistortion doesnt have the same bite,but the presentation
is relaxed andmusical, which none of the new ECC83types can match.
This valve does every-
thing it should do excellently.
CHINESE(Sold under various brands,recently discontinued. GP:4
7)Chinese 12AX7s tended to befitted by all the major
ampmanufactures while they werein production. On the plusside they
have good gain andlow microphonics, which suitsthe Boogie and the
Marshallamps. The drawback? Acomplete lack of tone, givingthe
trademark wasp in a jamjar cheap overdrive sound.The treble is
fizzy and thebass response gives a hazydistortion. Also, after
only
short periods of gigging these valvestend to sound harsh and
brittle. Sadly,we cant recommend these valves.
JJ TESLA (Slovak Rep, current. GP: 5 8)Watford Valves have
recently re-evaluated this valve (some earlyproduction items
produced excessivehum which rendered them useless). Thevalves gain
characteristics place it in themedium to high gain range. The
bottomend response is clean and clear; it has asolid structure
which makes it free fromadverse microphonics. Tonally, theyreare
great. The midrange has a slightblurring which seems to increase
theharder you push it, while the top end issweet and clear and has
nice sustain.Great for rock sounds, but not ideal forclean.
GE 5751(USA, NOS. GP: 6 12)This is a low-gain valve which
producesall the classic GE sound stage andperformance as described
with the12AX7WA version. The valve is very lowin distortion and
very difficult to clip. Thisis an excellent valve for use in
Fenders orany clean stage application, soundingbright and vibrant
with plenty of detail.Its very well balanced indeed its veryeasy to
get identically matched examples(where each of the twin triodes
haveidentical characteristics). This valve is farbetter than any
currently produced valvefor clean, pure Fender style twang.
RFT(former East Germany, NOS. GP: 8 14)This German valve used
for a longperiod by Marshall is sometimesbranded Brimar, Siemens or
Telefunken.It has a rich bass response, great drive, aclear and
detailed midrange and is verylow in microphonics due to a thick
glassenvelope. This valve distorts earlier thanthe USA types, but
it shows less trebleresponse a characteristic which lends itto
rock-style set ups. The rich harmonicdistortion, full of rich
sustain with plentyof bass crunch, makes this a great valvein
Marshall, Boogie and Vox amps.Definitely one for rockers and
bluesplayers.
TESLA E83CC/ECC803S(former Czechoslovakia, NOS. GP: 18 24)The
Czech replica of the famous
80
Mullard: king of preamp tubes A military grade Brimar CV4004
-
Telefunken ECC803S, this valve hasthe large A frame getter and
thickgrade glass which eliminatemicrophony. It also retains the
goldpins and plate structure of theTelefunken (and is not the same
asthe new JJ Tesla E83CC).
The first thing that strikes you isthat it is very quiet and
displays nomicrophonics whatsoever. Itsbeautiful on female vocals
in pro-audio applications as it has a supermidband, very fast and
dynamic. Wechecked these against a privatestash of real Telefunken
ECC803Sand now reckon that these areidentical in every way,
including thesound (all it really lacks is thediamond mark). It has
a rich bottomend, silky smooth treble and nicebalance.
In guitar amps the sound stage is big,with no rings and no pops
just yourguitar. This valve seems very neutral, notcolouring the
sound in any way, andwhen pushed into distortion it soundsreally
rich with super-late compression.This is fabulous it just does what
it issupposed to do: nothing more, nothingless.
SUPER TUBES: RESULTSThe first thing is that under these teststhe
unanimous conclusion is that theNOS valves offer better sound
qualitythan the current production types, butthis has to be
balanced against cost andwhat your own budget will allow.
Tonalityis in the ears of the listener and youmight find that a
current production itemhas exactly what you are looking for. Sotry
as many valves as you can until youfind the sound that suits
you.
The Mullard ECC83 is the clearwinner, as its own superb
charactershines through. Detail, sustain andperfect balance are
second to none, but
what really wins the day is its superbthree-dimensional
distortion characterand bass bite.
Otherwise, its a very close race forrunner-up. The RFT has a
great rock toneand Mullard-style gain: it can be made todistort
very easily and is most at home inMarshall and Boogie amps. With
basscrunch in abundance, this is an idealvalve for rock players.
The GE is themost American sounding due to itsbright nature. We
love the sound stageand crisp distortion of this valve, and
itscertainly a great all-rounder with lowmicrophony.
The Sylvania and Philips valves allshow a similar sound quality.
TheSylvania have higher gain and higherdrive: this could lead to
feedback incritical early gain stages if the valves areunselected
for microphony. The Philipsseems to be tighter in the bass area
butretains the classic mid-band warmth and it sounds really good in
Fender amps.
The Brimar CV4004 is a classicBritish-sounding valve. Refined
andbalanced, it does everything it should,
and very well. Mind, its not asaggressive as the Mullard, the GE
orthe RFT.
Of the current production items,in terms or pure sound quality
theJJ Tesla is the best. The current JJTesla valves (used heavily
byGroove Tubes) are higher gain thanones from the early
productionyears. They generally have a goodsound with a forward
presentation,though when pushed really hardthey can sound a little
rough aroundthe edges. The audio boys may notlike this but it does
sound good inguitar amps.
The Sovtek valves are certainlylow on microphonics and thatswhy
theyre used by more ampmanufacturers than any other valve.The WB
and LPS are the best for
guitar. The LPS seems to be cleaner andsharper than the other
Sovteks, and whatyou lose in microphonics you get backdouble in
terms of gain. This providesmore crunch, more drive and moremusical
tone than any Sovteks before.Basically, the Sovteks do tend to
sufferfrom a little midrange fuzz when pushedand lack the midrange
detail of NOSvalves, but they offer top value for moneyand are
available in quantity.
The simple rule to remember is that allthe valves do sound
different and it maybe the least expensive valve that meetsyour
needs. Once you have found yourpreference always get some
sparesbecause in life these three things arecertain: death, taxes
and the fact thatstocks of original vintage valves will dryup!
Next issue: current production and NOSoutput valves go under the
tonemicroscope.
Further results and other tube typescan be seen on the Watford
Valves website: www.watfordvalves.com
A M P T E C H
81
V alves are available from a numberof established UK dealers,
althoughprices vary according to supply,degree of testing and
matching provided,and so forth. You can generally expect topay a
quid or two more for guaranteedtested preamp valves than from
job-lotwholesale style sellers; youll have todecide for yourself
what the savings vsthe risk is worth to you. As these
testsindicate, many current Eastern Europeanvalves in particular
have occasionallyhigh failure rates, and even US and UK-built
valves of near-mythical status cansometimes fail right out of the
box.
Although many big valve dealers willre-brand units with their
own logos (as
done by Groove Tubes, Ruby Tubes, andWatford Valves own Harma
label) youshould always have access to accurateinformation on the
original modelnumber and country of origin. Asdiscussed in our
feature, all currentproduction valves will come from well-known
lines built in a few establishedfactories, while remaining supplies
ofNOS valves are also generally only fromfamiliar and traceable
production runs ofyears past whatever new branding isgiven them.
Many good guitar shopscarry stocks of valves, but for specialistUK
suppliers try:Watford Valves 01923-893270
orwww.watfordvalves.com
CONNECTIONS
GEs robust, low-gain 5751 Chinese 12AX7: not a favourite
-
H aving sorted you out for preampvalves last issue, this
installment ofTube Tasting turns the microscopeon the two major
styles of largeoctal (that is, eight-pin) output valves.
Mainly an American valve in its originalform though examples
were builtelsewhere, and of course currentproduction comes from
Eastern Europeonly the 6L6GC and its relative the 5881are most
closely associated with the bigFender amps rated at 40W or
more,though they also feature in newer designsfrom Mesa/Boogie,
Soldano and others.Its British cousin the EL34A (a somewhatsimilar
valve but with slightly differentvoltage requirements and
tonalcharacteristics) is the longest-runningvalve of choice for
Marshall, Hiwatt andothers, and typifies the classic Britishsound.
The two most popular smallervarieties of output valves the EL84
andthe 6V6GT will be examined next time inthe third and final part
of this series.
As in our last issue, our tests willcompare both current
production and NOS(New Old Stock) samples (turn back to Part1 for a
fuller explanation of terminologiesand the history of Western
verses EasternEuropean and Chinese valve production).GP stands for
guide price and indicatesthe approximate price range you canexpect
to pay for a single valve on the UKmarket (remember: most amps will
require
either two or four output valves).
TESTING: EL34By evaluating current production EL34against NOS
items, we hope youll beable to select the most suitable andreliable
valve for your style of music.Weve placed the emphasis on
currentproduction items which should be easyto get hold of and the
good news is thequality of current production EL34s hasgreatly
improved since the start of thedecade. Weve picked valves with
lowmicrophony, low noise and similar gaincharacteristics, using the
Mullard EL34as a reference valve. The same appliesnow as did years
ago: if you want theultimate tone, simply buy the Mullard ifyou can
find (and afford) them.
The amplifier we used was a Marshall100 Super Lead into a 4x12"
cab loadedwith Celestion Vintage 30s. The guitarswere a 73 Fender
Strat, a 1980 YamahaSA2000S semi-acoustic and a 1980 LesPaul
Standard.
MULLARD SINGLE GETTER(GB, NOS. Guide Price: 60 90)The Mullard
provides crisp ringingsustain and huge, tight bottom end
withclarity which was unrivalled in this test.The Mullard has it
all: the valves soundhuge with wide imaging and detail. When
the valve is pushed hard it soundsferocious with cutting bite.
Power chordsrock the very foundations, and the valvenever loses
control when saturated. Inhistory, not many valves can claim
themantle of best audio valve and bestguitar valve: the Mullard
still reignssupreme at both.
SOVTEK WXT(RUSSIA, current. GP: 6 12)The WXT is an upgraded
Russian valvewhich replaces the EL34G & EL34G plus.The
manufactures claim a unique gridblock design which improves
electronflow and gives higher output apparently6 per cent higher
than the competition.
With a rating of 25 watts platedissipation, this valve is a
vastimprovement on its predecessors. It hasa higher anode current
draw and highergain and is very stable. In reliabilityterms, the
valve has stood the test on theroad in countless Marshall amps and
inour high plate volt test, all 24 piecescome through with no
problems.
The valve has good bottom endresponse which is nice and tight.
Itdoesnt have a big sound stage like theMullard, instead offering a
one-dimensional focus which is great for leadwork as it pushes the
sound right out.When saturated, the distortion has afuzzy element
great for grunge. Thetop end response can go a little grainyand get
hard on the ear but generallytheres a nice top end chime.
Wedrecommend this valve for use in allapplications.
SVETLANA (Russia, current. GP: 8 14)The Svetlana claimed by its
makers togives the best performance underoverload conditions thanks
to a specialplate material is used by many OEMmanufacturers
including Marshall.Reliability is not a problem: this valve
hasstood the test of time. In our endurancetest all the Svetlanas
came through withflying colours. The thing that reallyimpressed us
was that the readingsdidnt change. Svetlana definitely havethe
ageing process sorted out.
The valve has a more linearperformance than cheaper options
likethe Sovtek, and the bass response isbetter defined. The sound
stage is alsobigger than the Sovtek, and gives theMarshall more of
the trad British rocksound. This unit is very well balancedwith the
midrange in correct focus, thetop end smooth and crisp. A great
valveand, again, thoroughly recommended.
EI & EI 6CA7(Yugoslavia, current. GP: 8 14)Both of these
Yugo valves failed theendurance test at an alarming rate even the
6CA7 versions which aresupposed to be specially tested by the
A M P T E C H
82
TUBETastingA Players Guide: Pt2Output ValvesWITHOUT FUNCTIONING,
GOOD QUALITY OUTPUT VALVES your5000 hand-built, point-to-point
Scream-O-Tone combo is just somuch crackling plywood. This issue,
Derek Rocco of WatfordValves shares with us his taste tests of the
larger variety EL34and 6L6GC power tube varieties
-
manufacturer. The valves that did comethrough (about 7 out of
12) weredrawing up to 10ma less current thanwhen we started the
tests. These wouldneed a serious burn-in process
beforematching.
Those which survived burn-in lackedthe bottom-end response of
the Mullard,Sovtek, Svetlana and Harma andsounded lighter and
woollier. Theres anice top end response which is notharsh and easy
on the ear, but themidrange response is recessedand very fuzzy when
pushed.
Overall, these are not asgood as the Sovtek or Svetlanaif you
want the classic rocksound and, basically, this valvejust isnt in
the same league asthe others, with poor reliabilityand electrical
construction.Best avoided.
JJ/TESLA (HARMAVersion)(Slovak Rep, current. GP: 8 15)The Harma
is a speciallytested/selected valve ofEuropean manufacture. It
hasthe widest frequency responseand the highest platedissipation
(30 watts) of the
valves tested. It has a number of featuressuch as gold wound
grids and heavygrade glass all making this a ruggedvalve for road
use.
The bass response is big and bold andvery well balanced. The
tone is brightand slightly forward-sounding, with asound stage
thats big and quite Mullard-sounding and a mid response thats
clearand sweet. When driven hard the valvenever loses control, with
rich distortionblasting through. We really love the top
end response it makes aMarshall really sing, and itseasy on the
ear. Reliability-wise, these are rock-solid: thebest current
production EL34,bar none.
CHINESE(Sold under various brandnames, current. GP: 5 10)Chinese
valves have a badname for reliability, beingelectrically
inconsistent and ofpoor build quality. Somedealers are saying that
theyveimproved, so we thought wedtry them again.
The results: as bad as ever.These are the only valves tohave
ever blown more than
one fuse on our test rig. Even when youfind some that actually
work they haveabsolutely no top end, sounding dull andunrefined.
Frankly, the box and theprinting is worth more than the
valveitself. Our advice? Dont bother.
EL34s: CONCLUSIONThe general standard of EL34s hascertainly
increased since the start of thedecade. The battle ground comes
downto three valves, all of which have theirown virtues: the
Sovtek, Svetlana and theJJ/Tesla. The other valve manufacturescant
currently compete.
The best-sounding current productionvalve is the JJ/Tesla (sold
by WatfordValves as the Harma STR version). Thiswe found the
closest to the Mullard insound quality and overall size.
TheSvetlana also has a great Mullard-stylebottom end but is not as
involving or asforceful as the Tesla. The Sovtek is agreat blues
valve which overdrives nicelyand pushes out fierce, hot solos.
Theycan sound grainy at the top end, but Idont mind that: after
all, its rocknroll.
The Mullard is still king of the pile,followed by the Siemens.
The gap isdefinitely getting closer, but its doubtfulthat the
Mullard will ever be bettered.Mullard prices continue to rise, so
if yourequire the ultimate then it wouldgenuinely pay to buy now.
If financiallychallenged then then the JJTesla/Harma, Sovteks and
Svetlana areall good choices which you can try untilyou find your
favourite.
TESTING: 6L6GC6L6 types are one of the biggest-sellingvalves in
American history, and are stillthe favoured choice of
manymanufactures. We wanted to see if thecurrent production types
could competewith some of the finest valves ever made.
The amplifiers used were a 70s FenderTwin Reverb fitted with JBL
speakers, a70s Twin Reverb fitted with originalFender blue back
speakers, and aMesa/Boogie Mark IV combo. Guitarsused were the same
as for the EL34 tests.
We chose the famed RCA 6L6GC wasused as a reference. The
JBL-fitted Twin with its piercing high end and overallvolume was
used to establish if thevalves were microphonic.
RCA BLACK PLATE(USA, NOS. GP: 50 80)The RCAs handle every
situation withgreat authority. From hard rock in theBoogie to
steely Fender twang, thesejustify their legendary reputation
andprovided an accurate reference standard.The bass is big with
perfect balance anddefinition between top, middle andbottom. Sonic
presentation is full andwhen the valve goes into distortion it
83
Old-version Tesla EL34
Lotta bottle: 6L6GCs power a Mesa/Boogie Rect-O-Verb,above,
while EL34s drive a Marshall head, below
-
A M P T E C H
remains sweet and musical. All the ampssound huge with RCAs and
displayed nota hint of harshness, even whensaturated. These valves
simply make youwant to play.
CHINESE(Sold under various brands, current.GP: 5 10)This valve
is offered by many amplifiermanufactures and many designer
valvecompanies. All we can say is: why? Afterfinding a choice
foursome to fit the Twin(after 10 valves failed a simple
burn-intest) the sound quality was still abysmal:harsh and brittle,
with compression waytoo early. The bass is loose and fizzy andin
the Fender with JBLs I found myselfthinking that a transistor amp
wouldsound better then the amp went down.On examination we found
thecathode/heater insulation was poor andthe valves were gassy,
whichever brandname was placed on them. They alsowere pretty
microphonic. It makes nocommercial sense for any dealer to
stockthis valve as they simply cannot operateat normal guitar amp
plate voltages. Ifyour amp has these valves installed,discard them
at the earliest opportunity.
SOVTEK 5881/5881 WXT(Russia, current. GP: 5 10)This is the
industry standard, fitted byFender, Marshall and Boogie. They havea
warm tone but lacks the scale andharmonic detail of the RCA.
Whenpushed hard the Sovteks tend to losecontrol and can sound
muddy. The finedetail is blurrier than the other valves,especially
with the JBL-loaded Twin. TheSovteks performed very well on
themicrophony test, and only a few unitsfailed the burn-in
test.
SOVTEK WXT Plus(Russia, current. GP: 7 12)This valve differs
from the 5881 by havinglarger plate dimensions and improved
grids to allow higher power handling, andit performed very well
in the microphonictests. The WXT Plus has more top endclarity than
the 5881: the midrange is stillmuffled when pushed, while the
bassresponse is much the same as the 5881,being soft and sweet. In
all three ampswe noticed a little more detail and claritythan with
the 5881, yet the WXT Plusvalves were not as good as the majorityof
others in this test in the claritydepartment.
SYLVANIA(USA, NOS. GP: 20 30)These Sylvania valves late-60s
andearly-70s production sound full andrich, and theyre solid as a
rock: noproblems on the high plate volt tests andno problems with
microphony. The bassis nice and tight with that classic warmsound
associated with Sylvania. In theFender amps they sound a lot
brighterthan in the Boogie but in no way are theyharsh. The
midrange is not as detailed asthe RCA, but the valves are very
punchyand forward sounding.
Imaging and presentation are far betterthan the Sovteks, too.
These are a greatchoice for all applications if you wantthat real
Fender twang.
GE (Early Type)(USA, NOS. GP: 22 32)The early type GE 6L6 has a
morerounded appearance and is slightly
smaller than later production items. Thesound stage and imaging
are huge,making the notes fly out of the amp.Bass is deep, rich and
plentiful andequally as extended as the RCA; thefamous Strat voice
is not lost even underdriven conditions. The top end has a
rich,bell-like clarity which begs you to sustaina note. In the
Boogie which came withpoor-quality Chinese 6L6 valves fittingthe GE
gave an instantly richer, fatter,almost stack-like tone which I
thoughtsounded better even than with the RCAs,while the JBL-fitted
Twin shone withclarity and midrange sparkle. These GEsare one of
the greatest 6L6s of all timeand come with our
strongestrecommendation.
TUNG-SOL 5881(USA, NOS. GP: 35 45)This is the valve that gave
the tweedFender Bassman its true voice. The bassis very tight, well
defined and in yourface: the valve is well balanced and hasthe
classic midrange twang. They giveless power than the Sylvania, GE
or RCAbut have superb drive and great earlydistortion and actually
make the ampsound bigger than it really is. A great-sounding valve
that deserves its classicstatus.
PHILIPS WGB (& HARMA SB)(USA, NOS. GP: 10 20)This
American-made military
84
Valve heaven: an original RCA black plate 6L6GC
A Russian-made 5AR4 rectifierand EL84 (left & centre) flank
anNOS small-bottle USA-made GE6L6GC (right), one of the
clearfavourites of the tone tests
-
specification valve has all the tight bassand midrange clarity
and twang of theTung-Sol and its something of abargain. The break
up is very musicaland the dominant midrange response isuniquely
classic Fender with noharshness. True, its a little less definedand
aggressive than the Tung-Sol, butits warmer with a touch less
bass.
This valve is superb in Fenders if youfancy midrange honk and
early distortionat club volume levels. These valves arean ideal
choice in reissue Bassmans,Boogies and Soldanos. The Harma SB-6L6
is a specially selected version of thePhilips.
HARMA STR(E. Europe, current. GP: 14 17)This is the best current
production 6L6.The glass envelope is made from highquality heavy
grade glass, making thevalve the most unmicrophonic of any
wetested. The gold-plated grids and specialplate alloy give it
improved platedissipation and greater stability at
highvoltages.
When it comes to scale of sound, theHarma STR is second only to
the GE. Thetreble response is full, smooth andcreamy, the sustain
long and pleasingwith punch and definition. This valve is areal
goodie: highly recommended.
SVETLANA (Russia, current. GP: 10 16)The Svetlana has a growing
list ofprofessional users. The specs claim adesign based on the
famousPhilips/Sylvania STR 387, and sureenough the extra thick mica
spacer doesmake this valve less prone tomicrophony.
In all test amps the balance wasperfect just like the RCA bass
is crispand clear but not as deep as the Harma.Distortion is sweet
with good punch, andwhen pushed this valve avoids themuddiness of
the Sovteks. We reckon itsthe best current production itemavailable
behind the excellent HarmaSTR reviewed above.
PHILIPS/SYLVANIA STR 387(USA, NOS. GP: 22 32These 387 valves are
famed for theirrugged construction and high voltagetolerances. In
sound terms we coulddetect no difference between the 387and the
Sylvania 6L6GC: indeed, thistube actually sounded brighter than
itsearlier brother, which I felt was over-bright in the Twin fitted
with JBLs.Overall, it has the same characteristicsas the Sylvania
and would be a verydecent choice.
EAST EUROPEAN/HARMA STR KT66(Russia, current. GP: 28 35)This is
a completely different valve fromthose built by Sovtek and
Chinese
factories in recent years and(somewhat misguidedly)labelled
KT66. This new run commissioned from RussiasReflector factory by a
leadingUS tube retailer but now alsoavailable under the Harmabrand
is accurately basedon the specs of the legendaryBritish GEC KT66,
thatessential ingredient in somany early Marshall amps,including a
rugged structureand gold-wound grids.
Tested somewhatseparately from the other6L6s in a vintage 59
FenderBassman, a reissue MarshallBluesbreaker and a reissue
FenderVibrolux, this valve proves stunning in allapplications. Bass
response is big, andthe sound is warm and very responsivethroughout
the range. In the reissueBluesbreaker it was actually hard to
hearany difference between these and anNOS pair of GEC KT66s
(costing from65 95 each on todays market, whenyou can find em).
Highly recommended.
6L6GC: CONCLUSIONWith 6L6 valves the first step is todecide how
you want the amp to soundin relation to your style of music.
Sometypes distort sooner, others stay tightand crisp and both can
be consideredexcellent tubes in their own right. It alldepends on
what youre looking for.
The Russian 6P3S and the Chinese6L6s are not worth fitting in
guitar amps.Most of them dont work: the ones thatdo sound poor.
The Russian-built Sovtek valves aremore reliable and make good
economicchoices for general repairs orreplacements, but they dont
havecharacter or tonal definition to comparewith NOS units.
The top two current production6L6GCs are the Harma STR and
theSvetlana. The Harma have a bigger GE-style presentation and are
more vibrant,
easily ranking alongsidemany USA valves.
Of a slightly differentbreed but an electronicvirtual equivalent
of the6L6 types, the new-model Russian KT66 isa welcome addition
tothe current-productionmarket, and puts toshame many
valvesmarketed as KT66s inrecent years. It you wantthe sound of an
originalGEC KT66 but cant paythat kind of money, thisis the only
realalternative.
The real stars of the NOS examplesare the early production GE
and, notsurprisingly, the RCA black plate. TheGEs bass is not as
deep as the RCAs,but would you really notice this with yourBoogie
or Fender cranked up to eightyour favourite club? I think not.
Thegreat thing about the GE is that the moreyou turn it up, the
bigger it gets. TheRCA is better balanced, but I wouldgladly trade
that for the more forward,slightly brighter sound of the GE.
Thistube is pure rocknroll.
The Sylvania 6L6GC proved itselfanother great valve: warm, rich,
full-bodied and an excellent choice for aFender Twin. With a Strat
in the out ofphase position, this was just heaven.
But the real revelation was the US-made military spec Philips
WGB/HarmaSB-6L6. It has less power than the otherUSA items, but an
excellently detailedmidrange presentation and theadvantage of early
break-up, giving big,fat distortion in a Twin Reverb withouttaking
your head off and, in the Boogie,a nice crunch with any amount of
pre-amp distortion. This valve is just the jobfor a club
player.
Next issue: small bottle EL84 and 6V6output valves. Further
results and othertube types on the Watford Valves website:
www.watfordvalves.com
85
Chinese 6L6GC: discard them
-
78
M any guitarists are turning on tothe fact that heavenly sonics
aremore easily achieved forrecording and small gigs bycranking up a
great 15 or 20 watt ampthan by piling mattresses against thedoors,
swaddling the walls in carpet liner,and trying to coax that 100W
MarshallPlexi or Fender Twin Reverb into its tonezone while
homicidal neighbours and thenoise police launch tear-gas into
yourstudio flat. Because they mimic thetonalities of their
respective olderbrothers but do so at significantly loweroutput
levels, these smaller valves areresponsible for some of the finest
tonesavailable without risking shattering youreardrums and your
tenants agreement inthe swipe of a single power chord.
Related in constructional and soniccharacteristics to the larger
6L6 types,the 6V6GT is the classic small-bottleAmerican tube.
Putting out from around 6to 15 watts each (depending on thecircuit
and transformers) compared to itsbigger brothers 15 to 30 watt
output, itendows Fender classics like the Champ,Princeton and
Deluxe with an easy,smooth distortion and raw, rich texture but
make no mistake: while a 6V6 will fit a6L6 socket, do not
substitute them in anamp not designed to do so. Theconsequences
could be very expensive.
Sonically aligned to the larger EL34though different in
construction most
notably housed in a slim, baseless, 9-pinbottle the EL84 is a
true British classic.Originally found most famously in vintageVox
amps and taken up by everyone fromMesa/Boogie to Matchless to
Orange toLaney in recent years, its a sweet andsparkling output
valve with easycompression and crystalline highs.
As with Pts 1 & 2, our tests willcompare both current
production andNOS (New Old Stock) samples; turn backto TGM vol 11
no 3 for a fuller explanationof terminologies and the history
ofWestern verses Eastern European andChinese valve production. GP
stands forguide price and indicates theapproximate price range you
can expectto pay for a single valve on the UK market(remember: most
amps will require eithertwo or four output valves).
TESTING: EL84To evaluate a range of EL84s, myself,Queen
guitarist Brian May and Brianspersonal tech Greg Fryer loaded
thevalves into a variety of Vox amps for twoseparate rounds of
testing, under bothnormal playing conditions and thehardest of
professional workingsituations. All valves were pre-selected tohave
the same plate current andtransconductance. GE and Mullard
EL84swere used as a reference.
Test 1: The amplifiers used were anoriginal Vox AC10 Twin fitted
with Elac
speakers and an original Vox AC4: for testguitars used we chose
a 1973 FenderStratocaster and a 1980 YamahaSA2000S
semi-acoustic.
Test 2: The second tests were carriedout by Greg Fryer and Brian
May atBrians home in the summer of 1998 andin rehearsals in
preparation for his 1998world tour. The Vox AC30s were fittedwith
Celestion Greenback, Vintage 30 andAlnico Blue speakers and Brians
famedtreble boost was employed, too). Thiswork led to the
development of our FullDrive test rig, with assistance from TGMamp
expert and Vox guru David Petersen.
MULLARD (GB, NOS. Guide Price: 20 40)The Mullard excelled in the
initial test andin the tests with Greg and Brian. Theyprovided
crisp, ringing sustain and hugetight bottom end with clarity
whichsounded larger than life, giving theimpression of space and
immense detail.It never seemed to lose control evenwhen Brians
treble boost was added;indeed, it seemed to get more punchyand
dynamic. Bass, middle and treblewere all in proportion. We all
agreed thisis a great valve and impressive instanding up to the
massive punishment itreceives inside Brians flat-out AC30s.
EUROPEAN STR(European, NOS. GP: 10 15) This valve has always, in
my opinion, gotas close to the Mullard as you could gowithout
buying a Mullard. Its got rich,creamy mids with a GE-style
soundstage, and the bottom end is tighter anddeeper than the
Sovteks. Under normalsaturated conditions this valve alwayssounds
in control, with sweet, cleartreble. Greg and Brian liked these
valvesfor the aggressive edge and musical toneunder treble-boosted
conditions.
SOVTEK (Russia, current. GP: 4 8)This current production valve
is used bymany leading OEM including Laney andPeavey. Generally we
find it has aroundhalf the anode current of a Mullard, andthe gain
is also a lot lower, but soundwiseits better and more reliable than
theChinese valves though it doesnt have agreat deal of bass, and
when pushedhard it tends to go muddy. In a regularlygigged amp we
suggest you buy two orthree sets, as theyll wear out. Great
forrepairers and hobbyists, though.
SOVTEK EL84M(Russia, current. GP: 5 10)The EL84M is a Russian
military surpluswhich is of more robust construction thanthe
standard item, with current drawtypical of what we would expect for
amilitary valve. In the amps this valvesounded fine with good
balance, and themidrange was more detailed than its
A M P T E C H
TAKE A LOOK BEHIND THE WORLDS FAVOURITE recording ampslike
Fender Champs and Deluxes, Vox AC15s and AC30s and themore
diminutive Matchless models and youll find these sweetbut hot
sounding small bottle tubes. This issue, Derek Rocco ofWatford
Valves shares his tests of EL84 and 6V6GT varieties with a little
help from some Brit-rock royalty
TUBETastingA Players Guide: Pt3 EL84 & 6V6GT
-
cheaper relation. With normal drive unitsthe valve sounded
aggressive with deepbass; with Brians treble boost themidrange
sound became very heavilycompressed. To my ear this soundedawful
with the Greenbacks, got betterwith the Vintage 30s and sounded
veryaggressive with the Blue speakers.
Not the refinement of the Mullard orPhilips, then, but it does
push the soloright out which recessed the bass andtop under heavy
distortion, and it has aunique mid-range honk that Greg andBrian
both love. Recommended.
GE 6BQ5(USA, NOS. GP: 18 24)Many American-made units will carry
a6BQ5 designation, the US code numberfor EL84 valves but theyre
exactly thesame thing. The GE valves have alwaysbeen a favourite of
mine and in the Voxamps they showed all the virtues: gain,balance
and huge sound.
With the treble boost in place themiddle thickened up it
soundedheavy and crisp without losingdefinition. With Brian playing
thefamous Queen runs the valve wasextremely touch-sensitive. This
is agreat valve and sounded superb inthe Vox AC30.
PHILIPS ECG(USA, NOS. GP: 15 24)In my own tests this was
myfavourite EL84. The valve hasplenty of bottom end, sweet
cleanmidrange, and a top end thatsbrighter than the Mullard.
Whenpushed with a Real Tube Driver,Ibanez Tube Screamer or
standarddistortion unit the valve has qualityand refinement,
providing cuttingsolos just on the edge of mayhem.
The treble response is sweet and clearwith plenty of definition,
but when Gregintroduced Brians treble boost the valvedid appear to
go over the edge somewhat(the change happened in the
midrangeresponse, which seemed to go wild:remember, though, that
the treble boostadds huge gain at line level and isselected for
certain frequencies, and thisshouldnt prove a problem for
othermusicians in any set up). Here we aredealing with the classic
trademark soundof a genuine guitar hero, and for hisapplications
the Mullard, which excelledin this area, got the vote (and Brian
canafford em). This is a great valve in allapplications.
JJ/TESLA (Slovak Rep., current. GP: 6 12)This valve was not part
of the test withGreg and Brian, but its sound quality isgreat: a
cross between the bright sweetsound of the Philips with the balls
of theMullard. Its not as high gain as the STR
and therefore gives a little moreheadroom, plus a nice rich
overdrivesound with clear top end response. Thebalanced
presentation makes this anideal choice.
EL84 TEST RESULTSCue the familiar conclusion: all three of
usagreed that the Mullard is the bestoverall valve, although the GE
also scoresvery well due to its big sonic spectrum.These two valves
can both be considereda true reference of the type. On the
otherhand, they are very pricey and you mightfind it hard to
justify the expensewithout your record company or someoneelse
picking up the tab! Greg and Brianboth liked the European STR which
in thetest we called NOS European (thoughbranded by Watford Valves
as the HarmaSTR) as we arent 100 per cent sure of itsorigin. This
is the closest in terms of toneto the Mullard and also the closest
interms of specification. .
The Philips EL84 is the best soundingin the Vox as its rich,
bright sound givesthe amp a cleaner edge. When the trebleboost is
applied the valve goes into megadistortion which I love but the
valvedoes not have the control of the Mullard.Of the current
production items theJJ/Tesla sounds brighter and cleaner innormal
operation than the Sovteks. Bothof these valves show good bass
andtreble response under normal distortedsituations, but in treble
boost mode theSovtek EL84M seems to handle thepunishment a little
better. They do soundmuddy in comparison to the Mullards butthey
never lose control, and they seembetter balanced than the JJ, which
seemsto go very middly.
Overall, there are many good sounding,reliable EL84s on the
market which cansuit all budgets and playing situations.
TESTING: 6V6GTThe 6V6GT is one of my favourite valves,but so
many modern amps that use it donot have the tone of those classic
tweedFender Deluxes one of the greatest
rocknroll amps of all time. We setout to find out why.
The amplifier used was a FenderPrinceton Reverb II Paul
Riveramodel a good amp to evaluate6V6 , being capable of
supplyingsome very crunchy modern soundsas well as vintage. To the
1973Fender Stratocaster and YamahaSA2000S we added a 1980 GibsonLes
Paul Standard.
RCA 6V6GT/A(USA, NOS. GP: 18 25)These were used as the
referenceand seem at home with single coilsor humbuckers. They
produce a fat,controlled bass with a strong midcharacter. The valve
has greatbalance and individual notes can
79
MullardSovtekPhilips
-
be easily distinguished even under heavydistortion every slight
variation of toneis accurately reproduced. When pushedhard the
midrange character distortsbeautifully, with clarity and
refinement.Valves from the 50s and 60s which arethe most sought
after. This is a hard valveto beat.
MAZDA(France, NOS. GP: 10 14)These are a 1950s French military
valvethat we decided to test at 500V DC plateand screen on our test
rig (well abovetheir rated maximums). Five hours laterthey were
rock-solid where others haddied a serious indication of the
unitssolidity.
Fitted into the Princeton the Mazdarocks, the sonic spectrum
big, thedistortion fat and punchy. The bassresponse is not as deep
as the RCA,mind, and it does sound slightly edgy.When overdriven
the valve has a raw,organic sound which I fell in love with;
itseems better suited to the grungy side ofrock. With a Les Paul
the sustain is fulland rich with no harsh edges you feelyoure
playing a wall of amps, not just alittle Princeton. These babies
are greatlittle blues valves and work well with thesemi-acoustic
Yamaha in both single andhumbucking mode. The valve doesntlose
punch or go muddy even wheneffects are introduced. We loved
them.
SOVTEK (Russia, current. GP: 5 10)Sovtek have some good valves
in theirline up, but sadly this in not one of them.It has trouble
in old Fender Deluxes as itcannot handle plate voltages of
muchabove 345V DC (indeed in tests manydied at 325V DC, so be
warned). Thevalve is very harsh-sounding with aninferior bass
response, and whenoverdriven it is very muddy. A goodmeasure of a
valve is, do your ears hurtafter prolonged use? Boy, with this
valveI was hurting.
STANDARD 6V6GTY(USA, NOS. GP: 16 24)With its brown base
andsemi-smoked glass this looksidentical to the RCA units(and was
possibly made bythem). The top end of thisvalve really sings; the
moreyou throw at it, the more itwants. Killer Kossoff-likesustain
is achievable with theamp really pushed, with noharshness. The bass
isbigger than the Mazda andkeeps full definition even onfast runs.
Balance is superb clear and precise and thevalve is at home with
countryor jazz. Thoroughlyrecommended.
PHILIPS (USA, NOS. GP: 10 18)This is identical to the valves
used byFender in the 70s and would have beenthe standard valve
fitted to the Princetonwhen new. Its a lot brighter than theMazda
or Standard and works very wellwith the Fender Strat. The amp
soundsthinner, however, due to the sonicpresentation being not as
large, and thesustain isnt as fat or as long-lasting asthe Mazda or
Standard. The bass is notas well-defined, either, but the tone is
stillrich and warm. A great rocknroll valve.
GE (LARGE & NUDE BASE)(USA, NOS. GP: 12 18)Watford Valves
currently stock two typesof GE: one with the pins straight out
thebottom like the Sovtek 5881 and one witha full base. Both valves
have the largegrey box plate, and we found the soundquality to be
identical when both areplaced together.
These have the characteristic GE sonicpresentation: big, fat and
proud. The topend response is noticeably less than the
Philips, with midrange twang morepronounced than any other. Its
a forward,in-your-face tube with great punch.Ideally suited to
country or steel guitar.
ELECTRO-HARMONIX 6V6EH(Russia, current. GP: 5 10)A newer
offering, this is a Russian unitcommissioned by Electro-Harmonix
toduplicate the design of the RCA (alsosold as the Harma 6V6GT STR)
and itholds its own surprisingly well against theclassic RCA.
Compared to the bright,well-balanced Philips the 6V6EH alsoperforms
well, with a nice top end sparklewhich is not quite as bright but
still greatfor that out-of-phase Strat sound. Whenpushed hard it
maintains control,sounding loud and clear. When fullysaturated the
EH is not as crisp andround in the midrange, but starts to blur
actually a great sound.
The EH doesnt have quite the hugesonic presentation of the Mazda
nor itsrefinement and it breaks up somewhatearlier but this gives
it a unique voicewhich will undoubtedly appeal to a lot of
people. The sustain is lovelyand singing sustain, thebreakup
rich with plenty ofbottom end slam, balancingperformance with fine
detail;whats more our tests so farprove its sturdy and well built.A
great addition to the market.
WESTINGHOUSE 6V6GTA(USA, NOS. GP: 12 20)These valves are marked
USAand come in the original box.These are for the Neil Youngfans
with fantastic bassresponse due to the bass-forwardness of the
valvessonic presentation. Whendistorted the bottom notes onthe
guitar are in full focus
80
A M P T E C H
Sovtek 6v6GTBrimar 6v6GTY/CV511 Philips 6v6GT
-
great for riffing or heavy Zep-style music.The top end is not as
detailed, but sustainis good and clear; the midrange seems alittle
recessed but Strat twang can still beproduced. This is definitely
for hardrockers.
SYLVANIA 6V6GT/A(USA, NOS. GP: 10 16)This is a very
warm-sounding valve thatsa little bass-light when compared to
theStandard or Mazda. The midrangeresponse is this valves real
voice, and theclarity and Fender twang shine through.Sustain is
warm and rich, if again not asforward as the Mazda. When pushed
hardthe bass seems to become less definedbut the valve still
retains a very musicalsound.
BRIMAR 6V6GTY/CV511(GB, NOS. GP: 7 16)We have recently seen a
lot of dealerstrying to make a market in these bysaying that they
are a super hi-fi valveand great guitar valve, with high prices
tomatch. If you want a hi-fi valve, the Mazdastamps all over
this.
In guitar amps the Brimar is atraditionally British-sounding
unit. Thebass response is lighter than the RCA,Mazda or
Westinghouse and it has a verysmooth, laid-back sound with
noharshness. It doesnt have the get up andgo of most of the other
valves tested,which is a shame, though the clearmidrange never gets
flustered, even withheavy rock. Rock solid stability and agood all
round valve ideally suited,maybe, to jazzers.
VISSEAUX (France, NOS. GP: 10 16)This is another French military
valve witha lot of the same characteristics of theMazda. It has
rich sustain with good bass not as deep as the RCA, Standard
orWestinghouse, but about the same as theMazda. Like the Brimar,
the mids are verysmooth and controlled without theMazdas raw edge.
The top end responseseems recessed compared to the Philipsor Mazda,
but theres still plenty oftraditional Fender twang on tap
andsustain superb, rich and clear. This valveis very well balanced
and would be agood choice for all applications.
6V6GT TEST RESULTSThe first rule when fitting 6V6GTs is to
avoid the Russian 6p3s valve which anAmerican designer valve
company re-brands as there own 6V6HD. In ourexperience this version
is a poor unitwhich is also very hard to bias. This valveis also
sold by many UK dealers under theguise of 6L6GC, 6L6GT and 6L6GB.
Wedo not recommend fitting any of these.The more commonly seen
Sovtek 6V6GTreviewed above is poor in the soundquality department,
so the best alternative
by far for current production 6V6s is theRussian-made
Electro-Harmonix 6V6EH,a laudable copy of the classic RCA. The6V6EH
is one of the best valves of its typeto be produced since the
1960s: itprovides balanced performance with finedetail and offers
credible performanceboth in clean and distorted modes. Thisvalve is
important as it provides a current-manufacture 6V6GT that can be
fullyrecommended, and gives the OEMs thechance to produce a
great-sounding rockand blues amp that could put tone backat your
fingertips so lets see them do it!
Taking in the entire field, however, theRCA is still the valve
to beat, but twoothers come very close: the Mazda6V6GT and the
Standard 6V6GTY, andthe former is not badly priced by anymeans
either. The Mazda really rocks fromZep to Muddy Waters. It has a
raw, wild
feel and makes you want to play theguitar and feel good and it
makes iteasy to get a great sound quickly. TheStandard 6V6GTY does
everything thatthe Mazda but with more control; push itharder and
harder and it simply shoutsback, Give me more! Its huge bottomend
response is clear as a bell. These are1958 production and are
identical to theRCA that we used as a reference. Underheavy
distortion the valve just seems toget bigger, with a sustain that
is simplyremarkable.
The new Electro-Harmonix valve aside,this market remains
dominated by NOSunits, but fortunately these out-of-production
examples are generally lesscostly than NOS 6L6s or EL34s, with
theMazda, Brimar, Philips and even GE withinreach of most players.
Try a few setsbefore they are all gone.
81
These tests were conducted with thespecific aim of determining
the finepoints of valve characteristics andperformance with the
central goal of tellingyou which will be the best-sounding
andlongest-lasting components for a variety oftastes and
applications. Over the course ofthese three articles it might have
lookedliked our reviews have been splitting hairsover certain
matters comparing ultra fine-tuned sonic nuances which might be
virtuallyundetectable to many players but as witheverything we do
at TGM, if a product isworth testing, its worth testing
thoroughly.
The difficulty that open field reviewspresents us, however, is
that very often themore expensive items prove the superior.Thats
been no different through the courseof these Tube Tasting features,
where ninetimes out of ten (though by no meansalways) we found you
get what you pay for.That leaves us in the awkward position
ofappearing to suggest that in order to achieveany half-decent tone
you need to re-mortgagethe house to invest in a quartet of
Mullardsor RCAs. Not so. If your budget is limited, itwont always
be advisable to spend largesums on valves which, by nature,
willeventually burn out however good they are.(Think of them like
fine wine: as soon as youstart enjoying them, theyre on a
countdownto extinction. Then again, whats the fun of
leaving them racked up in the cellar? What adilemma)
Other more affordable types might beperfectly suitable to your
needs, so dontfeel you must have the most expensiveoptions to be
happy with your amp.Comprehensive testing available today canweed
duff budget units from good, and manyaffordable current production
valves fromSovtek, JJ Tesla and Electro-Harmonix amongothers can
sound extremely good indeed. Ifyoure gigging your Vox AC30 three or
fourtimes per week plus rehearsals with no bigrecord deal to foot
the bills, its probably notworth risking burning up 160-worth
ofMullard EL84s or 80-worth of Philips ECGson a pub full of sweaty
punters who wontnotice the difference five pints into the set;but
40-worth of JJ/Teslas might soundrighteously rocking, and end up
lasting youtwo years anyway (and if you want to treatyourself to
the Mullards, maybe tuck themaway for recording and special
occasions). Inshort, these things will blow up eventually,however
good they are, so dont spendbeyond your means just for the sake of
it.
Finally, thanks again to Derek Rocco andthe others from Watford
Valves and beyondwho contributed to Tube Tasting, withoutwhom these
features would not have beenpossible.
Dave Hunter
MUST YOU SPEND A FORTUNE?
-
1GROOVE TUBES
Le spcialiste amricain des lampes depuis 1979
-
2Les guitaristes dhier et daujourdhui ont un point commun :
lutilisation des amplis lampes. Malgr les avances technologiques
dans le domaine des amplis transistors, les guitaristescontinuent
leur prfrer les amplis lampes. Quest-ce qui diffrencie la
technologie lampes de latechnologie transistors ? Les lampes
offrent un son et une sensation de jeu diffrente tout
simplementparce quelles fonctionnent diffremment.
Quest-ce quune lampe ? Une lampe est un composan